Hostname: page-component-848d4c4894-cjp7w Total loading time: 0 Render date: 2024-07-01T22:30:20.587Z Has data issue: false hasContentIssue false
  • English
  • Français

Pyroxene accumulation in spinifex-textured rocks

Published online by Cambridge University Press:  01 May 2009

I. H. Campbell  and
N. T. Arndt
I. H. Campbell
Affiliation:
J. Tuzo Wilson Research Laboratories, Earth and Planetary Sciences, Room 3032, Erindale Campus, University of TorontoMississauga, Ontario L5L 1C6, Canada
N. T. Arndt
Affiliation:
Max-Planck-Institut für Chemie, Saarstrasse 23Postfache 3060, D-6500 Mainz, West Germany
Get access Rights & Permissions [Opens in a new window]

Summary

Natural pyroxene spinifex-textured rocks, free of olivine, may have MgO contents as high as 15%. If these rocks are allowed to crystallize in the laboratory under equilibrium conditions, olivine is the liquidus phase at 1350°C and pyroxene does not appear until the temperature has fallen to 1180°C. A similar problem is encountered in high MgO komatiites. If spinifex-textured and aphyric komatiites from Munro Township are plotted on an MgO-CaO-Al2O3 diagram, olivine control is evident until the MgO content of the melt falls to 15%. At this point the liquid trend moves away from the CaO-MgO boundary, indicating the crystallization of pyroxene. If a high MgO komatiite is crystallized in the laboratory under equilibrium conditions, pyroxene does not appear until the MgO content of the liquid reaches 9%. It is suggested that experimental and natural systems behave differently because pyroxene has crystallized metastably in the natural system under conditions of extreme supercooling. The early metastable crystallization of pyroxene can only affect the liquid trend if the spinifex zone contains a cumulate component.

Type
Articles
Information
Geological Magazine , Volume 119 , Issue 6 , November 1982 , pp. 605 - 610
Copyright
Copyright © Cambridge University Press 1982

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Andersen, O. 1915. The system anorthosite-forsterite-silica. Am. J. Sci. 4th series 39, 407–54.CrossRefGoogle Scholar
Arndt, N. T. 1976. Melting relationships of ultramafic lavas (komatiites) at one atmosphere and high pressure. Yb. Carnegie Instn. Wash. 75, 555–61.Google Scholar
Arndt, N. T. & Fleet, M. E. 1979. Stable and metastable pyroxene crystallization in layered komatiite flows. Am. Miner. 64, 856–64.Google Scholar
Arndt, N. T., Naldrett, A. J. & Pyke, D. R. 1977. Komatiitic and iron-rich tholeiitic lavas of Munro Township, Northeast Ontario. J. Petrol. 18, 319–69.CrossRefGoogle Scholar
Barnes, S. J., Coates, C. J. A. & Naldrett, A. J. (in the press). Petrogenesis of a Proterozoic nickel sulfide komatiite association: the Katniq Sill, Ungava, Quebec. Econ. Geol.Google Scholar
Bowen, N. C. 1914. The ternary system diopside-forsterite-silica. Am. J. Sci. 4th series 38, 207–64.CrossRefGoogle Scholar
Bowen, N. C. & Andersen, O. 1914. The binary system MgO-SiO2. Am. J. Sci. 24, 177–213.Google Scholar
Campbell, I. H. 1978. Some problems with the cumulus theory. Lithos 11, 311–323.CrossRefGoogle Scholar
Campbell, I. H., McCall, G. J. H. & Tyrwhitt, D. S. 1970. The Jimberlana Norite, Western Australia-a smaller analogue of the Great Dyke of Rhodesia. Geol. Mag. 107, 1–12.CrossRefGoogle Scholar
Jackson, E. D. 1961. Primary textures and mineral associations in the ultramafic zone of the Stillwater Complex. Prof. Pap. U.S. geol. Surv. 358, 1–106.Google Scholar
Kushiro, I. 1972. Determination of liquidus relations in synthetic silicate systems with electron-probe analysis: the system forsterite-diopside-silica at 1 atmosphere. Am. Miner. 57, 1260–71.Google Scholar
McBirney, A. R. & Noyes, R. M. 1979. Crystallisation and layering of the Skaergaard intrusion. J. Petrology 20, 487–554.CrossRefGoogle Scholar
Smith, H. S., Erlank, A. J. & Duncan, A. R. 1980. Geochemistry of some ultramafic komatiite lava flows from the Barberton Mountain Land, South Africa. Precambr. Res. 11, 399–415.CrossRefGoogle Scholar
Wager, L. R. & Brown, G. M. 1968. Layered igneous rocks. Edinburgh: Oliver and Boyd.Google Scholar